1. Field of the Invention
The present invention relates to optical data storage systems. In particular, the present invention is a file management system for interfacing a host computer to an optical data storage system.
2. Description of the Prior Art
Along with the computer came the need for high speed and high density digital information storage and retrieval systems. Magnetic disk drive systems, including both hard and flexible (floppy) disks were developed to meet these requirements. Magnetic disk drive systems of these types are currently in widespread use, and are well known.
The decreasing costs and increasing performance of semiconductor lasers has stimulated interest in the development of optical data storage systems. While these systems are conceptually very similar to magnetic information storage systems, component and media characteristics (e.g., optical transducers and storage disks as opposed to magnetic transducers and storage disks) of optical data storage systems are considerably different.
Magnetic and optical data storage systems typically include a controller which interfaces the host computer to the data storage system. The controller receives commands and data from, and provides status and data to, the host computer. In response to the commands, the data storage system controller provides signals which control the writing of data to and reading of data from the data storage disk.
Included within memory of the host computer is a disk operating system or file management system which interfaces file commands of a user (e.g., through user programs) and the commands recognized by the controller of the data storage system. Tasks performed by the file management system include keeping a directory of the location of all files of information data on the storage disk, and keeping track of remaining free space on the disk. In magnetic data storage systems, data written to the magnetic disk can be erased and rewritten, and therefore updated. The file management system therefore causes directory data to be written to predetermined locations on the magnetic disk. As files of information data are added to the magnetic disks, the file management system simply adds directory data to the reserve directory region. If a previously written file is updated, the file management system can erase and update previously written directory data.
Due to the characteristics of optical data storage systems, the file management systems typically used with magnetic data storage systems are incapable of interfacing the host computer to an optical disk drive. As a result, a separate file management system must be included within the host computer for this purpose. In write once read mostly optical disk drive systems, for example, data can only be written once to any location on the optical disk. Directory data cannot, therefore, be updated are previously written locations. Each time one or more new files of information data is written to the optical disk of the write once read mostly optical data storage system, the file management system must write directory data associated with these files at a new location on the optical disk.
In one prior art technique, files of information data are written to sequential sectors on the optical disk starting at an outer edge of the disk. An information region is therefore created on an outer portion of the disk, and expands inward as information data is written thereto. Directory data is written to sequential sectors of the optical disk beginning with sectors on an inner edge of the optical disk. A directory region is therefore created on an inner portion of the disk, and expands outward as directory data is written thereto. The disk is filled when the directory and information data meet. Since the directory data can be physically located at a point on the optical disk which is distant from the information data, the access time, or time acquired to write data to and read data from the optical disk, is relatively high. This file management system therefore reduces overall system performance.
Consequently, there is a continuing need for improved file management systems for optical data storage systems. A file management system which causes directory data to be written to directory data regions on the optical disk which are physically located near the information data regions would be desirable. Access time could thereby be reduced, increasing overall system performance. The file management system should also write directory data in a form which enables all previous versions of updated files to be found. Space on the optical disk could also be more efficiently utilized if directory data was written in such a form that only directory data to just written groups of files need be written.